The present invention relates to the cooling of dynamoelectric machines, and more particularly to cooling the stator core end regions of machines of large size such as turbine generators.
In large synchronous machines, the currents in the end turn portions of the rotor winding and in the end portions of the stator windings have magnetic fields which combine to produce an axially-directed magnetic flux. This axial flux enters the end of the stator core in a direction generally perpendicular to the core laminations, and causes relatively large eddy currents in the end regions of the core since the core is not laminated in a direction to minimize these currents. The corresponding losses may be quite large, and often cause excessive heating in the end regions of the core which may be sufficiently severe to require undesirable limitations on the maximum rating obtainable from the machine. Furthermore, the loss tends to be concentrated at the surface of the stator teeth, due to the skin effect, so that the hot-spot in each tooth is at or near the surface of the slot wall, and the highest temperature portions of the teeth are thus in direct contact with the insulation of the stator windings, which tends to heat the insulation above the maximum permissible temperature and thus shortens its life. Conventional cooling systems do not substantially reduce this excessive heating in the core end regions, and it has remained a serious problem in the operation of large machines.